Adhesive skin barrier materials are widely known in the medical field for use in ostomy faceplates, wound dressings, and skin-contacting gaskets or liners of various shapes and sizes, all of which may be generally referred to as hydrocolloid-containing wafers or dressings. A characteristic feature of such wafers is the presence of a skin-contacting layer of a soft, pliant adhesive material which has both dry and wet tack and which contains a dispersion of hydrocolloid particles capable of absorbing aqueous fluids and of swelling as such absorption takes place. One side of such a wafer usually has a cover layer of film or fabric, and the opposite side of the barrier layer is protected until use by a release sheet of siliconized paper or other suitable material. An example of one such wafer or dressing is disclosed in U.S. Pat. No. 4,738,257.
U.S. Pat. No. 4,738,257 discloses a wafer in which the hydrocolloid-containing adhesive layer is of substantially uniform thickness, but in recent years contoured wafers have become available in which the hydrocolloid-containing layers are not of uniform thickness. U.S. Pat. Nos. 5,133,821 and 4,867,748 disclose contoured wafers in which the hydrocolloid-containing barrier layers have relatively thick central body portions but then taper outwardly to terminate in peripheral edges or flanges of reduced thickness.
Whether contoured or not, all such wafers are believed to be produced in essentially the same way. A hydrocolloid-containing barrier material is simply extruded onto a web (which, following die cutting, may ultimately become the removable release sheet or the cover sheet for the finished wafer) and is then covered by a second web (which, following die cutting, may become the other outer layer for the wafer). If the wafers are to be contoured then, as disclosed in U.S. Pat. No. 5,133,821, the contouring operation may be undertaken prior to addition of the second web. Such contouring may be achieved by means of a roller (as in U.S. Pat. No. 5,133,821) or by a vertical press but, in either case, the contouring operation is performed on what is in effect a multi-layer sandwich in which the hydrocolloid-containing core layer of that sandwich has been extruded.
There are major disadvantages to a process requiring the extrusion of hydrocolloid-containing barrier materials, some of which have been well recognized in the past and others of which are only now being discovered. Skin barrier materials are generally expensive and substantial quantities of such materials are necessarily wasted because they become scrap in the final die-cutting operations. Wastage is particularly evident where the wafers are circular in outline, but such wastage also occurs to a substantial extent even for wafers of more rectangular shape.
Another disadvantage lies in the fact that making a contoured wafer with extruded barrier material is essentially a two step operation, the first step being the extrusion of a layer of barrier material of uniform thickness and the second step then being the compression of the barrier material into the desired contour. The requirement for successive processing steps provides its own complexities in terms of operating procedure and the physical size of the production equipment required. Additional problem areas involve keeping the freshly-extruded barrier material from sticking to the contouring roller. As disclosed in U.S. Pat. No. 5,133,821, a web of processing paper may be interposed between the barrier material and the contouring roller to prevent such sticking from taking place but, in that case, the processing web is generally stripped from the barrier after the contouring procedure and must be replaced by a web of different material which ultimately becomes the cover film of the final product. The need to use different web materials for processing (contouring) and for producing the final film (because the physical characteristics of the processing paper used for contouring may not be the properties desired as the outer film in the final product) presents additional complications and added expense.
In general, production methods for making adhesive wafers from extruded skin barrier materials require high-production equipment and long production runs with a minimum of interruptions. The very nature of such operations make quick changeover and interrupted operations difficult and impractical. The result is that specialized products of more limited demand, but nevertheless fulfilling important patient needs, may not reach the marketplace because production realities preclude their manufacture.
Finally, extrusion of skin barrier materials is now found to have a further disadvantage relating to the final products, their physical characteristics, and their performance. In the manufacture of extruded materials there is what is commonly known as "machine" direction and "cross" direction. The process of extrusion tends to orient molecules (also fibrous particles that may be included in the barrier composition) longitudinally in the direction of extrusion. Such parallel orientation means that properties that may be important in the performance of a wafer or dressing when it is used by a patient may not be uniform but instead may vary considerably depending on whether such properties are being measured in the machine direction or in the cross direction. For example, FIG. 1 depicts a barrier layer (exclusive of cover or release layers) of a conventional extruded wafer of uniform barrier thickness. The machine direction M is schematically illustrated by tiny striations oriented in parallel with the direction of extrusion, whereas the cross direction C is at right angles to the orientation of the striations. Such striations may take the form of filler particles of cotton or other fibrous additives, but such striations also represent the predominant direction of molecular orientation so that, even without the inclusion of a fibrous filler, properties in directions M and C tend to be different. Where such properties affect the strength of the barrier material (both prior to and following hydration), or the tendency to shrink in storage, or the rate of absorption or erosion, or the routes of saturation, swelling and/or leakage, the lack of uniformity in one direction versus another may have serious shortcomings.